1. Field of the Invention
The present invention relates to a lens barrel used in an optical system.
2. Related Background Art
In a small-sized camera having a multi-focal-point lens(zoom lens), the barrel is expanded and contracted to change the distance between an in-barrel lens (lens group) and a focal surface and hence the magnification (hereinafter, also referred to as zooming). At this time, the lenses in the barrel are divided at least into two groups to change the distance between the lens groups to a distance suited for each zoom ratio. Also, the action of image focusing (hereinafter, also referred to as focusing) is required for any magnification. Focusing is made by changing the position of the in-barrel lens relative to a focusing plane.
In order to expand and contract the barrel, the barrel has conventionally been made in a structure comprising a plurality of tube members. For example, there is as one example a technology described in Japanese Patent Laid-open No.H5-11310. The lens barrel described in this publication has first and second tubes sliding in an optical-axis direction of the optical system, and a base for accommodating therein the first and second tubes. The first tube is allowed to protrude from the interior of the second tube toward a subject side, and the second tube is allowed to protrude from the base toward the subject. Also, a single motor as a drive source is provided to slide both the first and second tubes. A first feed screw mechanism is provided in the second tube to slide the first tube due to a drive force of the motor. Furthermore, a second feed screw mechanism is also provided in the base to slide the second tube due to a drive force of the motor.
The expansion-and-contraction mechanism of the barrel described in the above publication is devised as in expanding and contracting the barrel by the single motor, realizing an increase of part density and integration and further achieving a low-cost due to reduction in part count. However, the increase in density and integration for parts is further advanced for the interior of optical apparatus and such tendency is conspicuous for the small-sized cameras. Under such situation, saving of space is desired for the barrel expansion-and-contraction mechanism. Therefore, the object of the invention is to provide a lens barrel having an expansion-and-contraction mechanism high in space efficiency.
Furthermore, the above publication describes a plurality of lens groups wherein movement control for the lens groups is performed in a general manner, i.e., the distance between the lens groups is changed during focusing or changing the zoom-ratio. However, another motor is arranged in addition to the motor for barrel expansion and contraction, in order to change the distance between the lens groups. The arrangement of two motors nearby the lens is an impediment to density and integration increase and forms a factor requiring a corresponding cost. The second object of the invention is to provide a lens barrel, which has a single motor to perform both barrel expansion/contraction and distance change between the lens groups thus realizing an increase of density and integration as well as cost reduction.
According to the present invention, a lens barrel of comprises: first and second tubes slidable in an optical direction of an optical system, a base for accommodating the first and second tubes therein, a single motor as a drive source to slide both the first and second tubes, a first feed screw being provided in the second tube to slide the first tube due to a drive force of the motor, a second feed screw being provided in the base to slide the second tube due to a drive force of the motor, and a drive gear to transmit a drive force of the motor to the first and second tubes. The drive gear comprises a cylindrical gear and a shaft gear having a shaft inserted in said cylindrical gear The cylindrical gear and the shaft gear rotate about a common rotation axis. The first tube is allowed to protrude from an interior of the second tube toward a subject, and the second tube is allowed to protrude from an interior of said base toward the subject. The cylindrical gear is interposed between the first feed screw and the motor, and the shaft gear is interposed between the second feed screw and the motor.
Preferably, a pair of first and second gears are included. They rotate about a common rotation axis. The first gear is interposed between the shaft gear and the motor, and the second gear is interposed between the cylindrical gear and the motor. Any one of the first gear and the second gear has an elongate hole formed in a circumferential direction and the other has a protrusion protruding into the elongate hole.
More preferably, a first lens group and a second lens group are included. The second lens group is movable relative to the first lens group within the first tube by a cam mechanism and protruding movement of the first tube from the second tube. The cam mechanism is made between the first tube and the second tube.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.